1. Field of the Invention
This invention relates to bioreactors and, more particularly, to a bioreactor mounted on a dual axis support structure to provide an aseptic, continuous flow bioreactor which eliminates the need for seals, internal mixing devices and the like.
2. The Prior Art
Biological processes are used for numerous commercial purposes ranging from production of food items such as cheese, flavorings, beverages, artificial sweeteners and the like, to non food systems such as systems for waste treatment and digestion, and mineral recovery, to name a few. In each of these applications, as well as numerous other biological systems, there is a need for an apparatus and method that will conveniently enable an operator to monitor and control various parameters of the biological system. The parameters of interest include pH, temperature, type and rate of gas introduction into the system, and degree of agitation.
Microbial systems can be valuable for numerous commercial purposes once the proper microbial agent or mixture of microbial agents has been identified and the optimum operating conditions quantified for that particular system. The operating conditions include temperature, pH, and the type and rate of introduction of gases, if any, introduced into the system. The digestion times for the various types of ores under these different operating conditions along with the selected microbial agents specifically determined to have an affinity for the particular system under consideration can be readily determined using this system.
Various low grade ore bodies such as those containing rare metals such as gallium can be processed economically with large scale microbial systems. One processing technique, for example, involves creating a large basin several thousand square meters in area. The surface of the basin is covered with an impervious membrane such as plastic or asphalt. Fractured ore is heaped on the basin and then leached using selected microbial agents, acids, and the like. The microbial agents digest the ores releasing the metals into the solution which percolates downwardly to the basin. A drain below the basin carries the solution to the further processing system.
Clearly, such a processing strategy involves the movement of massive quantities of ore so that even though the ultimate processing strategy of using a microbial-based leach is relatively inexpensive, the material handling costs to establish the leach dump will be costly if the values recovered are less than optimum. Once the leach dump with its thousands of tons of ore has been constructed, it is extremely costly to experiment with various microbial agents to attempt to determine the optimum operating parameters for that particular ore. Accordingly, it is critical to the success of any large scale microbial processing scheme to establish the optimum operating parameters for the selected microbial agents.
The desirable course of action is to use a compact bioreactor system holding a relatively small quantity of ore, say, one or two kilograms. This system is one that can be carefully monitored under selected operating conditions and with predetermined types of microbial agents. This type of bioreactor provides accurate data that can be determined relatively inexpensively and fairly quickly from a significant number of sample runs in order to optimize the microbial reaction conditions.
Conventional bioreactor technologies are disclosed in references such as Stockton et al (U.S. Pat. No. 4,892,707); Eppstein et al (U.S. Pat. No. 4,680,267); Matsumoto et al (U.S. Pat. No. 4,552,724); Wallin (U.S. Pat. No. 2,917,372); Biller (U.S. Pat. No. 3,131,212); Kersting (U.S. Pat. No. 3,274,075). Each of these references is directed to particular parameters of the microbiological process such as pH, temperature, mixing rates, gases, nutrients, etc.
Generally, the mixing action in these devices is provided by an impeller inside the reactor vessel either singly or in combination with a gas sparging system by which the various gases are dispersed into the liquid medium. However, particularly for those bioreactor systems having a high solids content, impeller erosion and/or damage is a determining factor as to the types and amounts of solids that can be processed in the conventional bioreactor.
Another important aspect of a bioreactor system is the need to have the capability for continuous flow of nutrients and/or reactants through the reactor vessel. Various systems of the prior art have been designed to meet this requirement. However, certain biological systems are highly prone to "infection" from the presence of unwanted microorganisms so that it becomes critical that adequate steps are taken to assure that the reactor vessel is suitably protected against the inadvertent introduction of infectious microorganisms. Further, the presence of stirrers, openable covers, shaft bearings, and the like, each represent a potential for inadvertent introduction of these infectious microorganisms.
Stirring itself, becomes a critical problem particularly in systems designed to handle particulate materials such as coal, tar sand, ores, and the like. Not only is the stirrer subjected to erosion through abrasion from these particulate materials, but the abraded particles from the stirrer could interfere with the analysis or even operation of the specific biological system. Stirrers also contribute unwanted shear forces in biological systems designed around the growth of filamentous microorganisms.
Continuous flow has been achieved in certain types of centrifuge apparatus. A number of prior art references are known that teach the basic concept of a dual axis mounting system to achieve continuous flow. The devices taught by these references are primarily directed toward centrifugal fluid processing systems. One such reference is that of Kobayashi (U.S. Pat. No. 4,296,882) which discloses a centrifugal separator for fluids such as blood. The container is mounted on a rotor rotatable about a vertical axis. The container is also independently rotatable about its own horizontal axis. In view of the high rates of rotation required for centrifugation, particularly for materials such as blood, the conduit leading to the separation chamber passes through the axis of the vertical shaft.
Other centrifugal liquid processing apparatus are disclosed in the references of Lolachi (U.S. Pat. No. 4,113,173): Brown (U.S. Pat. No. 4,114,802); Larsson et al (U.S. Pat. No. 4,372,484); and Ito (U.S. Pat. No. 4,425,112). In each of these references, flow through the centrifuge head is supplied by a flexible conduit passing through the vertical axis.
Further, it is well known that the forces required to accomplish separation of blood constituents, for example, are substantial unless one is using a unique dual axis continuous flow centrifugation apparatus shown in the reference of Brimhall et al (U.S. Pat. No. 4,874,358).
In view of the foregoing, it would be a significant advancement in the art to provide a bioreactor apparatus and method having the capability to process a continuous flow of materials through the bioreactor vessel in the absence of openings, or the like, which may expose the contents of the bioreactor vessel to inadvertent contamination from other microorganisms. Another advancement in the art would be to provide a bioreactor system that is subjected to continuous stirring at all times, and, more importantly, introduce the stirring action in the absence of stirrers, impellers, and the like. Such a novel bioreactor apparatus and method is disclosed and claimed herein.